Soil Science Society of America Journal Soil Sci. Soc. Am. J. 77:914–928 doi:10.2136/sssaj2012.0269 Received 22 Aug. 2012. *Corresponding author (robert.boddey@embrapa.br). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Soil Carbon Stocks under Productive and Degraded Brachiaria Pastures in the Brazilian Cerrado Soil & Water Management & Conservation T he Cerrados region of Brazil is regarded as the new agricultural frontier. Since 2000, the area under soybean in Brazil has expanded from 13.6 to over 27 Mha today, and sugarcane from 4.6 to 9.8 Mha (IBGE, 2013). Almost all of this expansion in area of soybean and some of the sugarcane has been in the Cerrado region and most has replaced low-productivity Brachiaria pastures. As both of these commodity crops are sources of raw material for biofuel produc- tion, considerable attention has been given to possible change in soil C stocks in- duced by land use change (Batlle-Bayer et al., 2010; de Figueiredo and La Scala, 2011). Moreover, the Low Carbon Agriculture Plan of the Brazilian Government aims to support farmers to recuperate degraded pastures to improve the efciency of beef and milk production besides the mitigation of GHGs through soil C se- questration and reduction in methane emissions (Brazil, 2012). Tere is, therefore, a great demand for data on soil C stocks under productive and degraded pastures in comparison with those under the native Cerrado vegetation. From the 1960s onward, forage grasses of African origin, mainly Brachiaria spp., were planted in extensive areas of the Cerrado region and today are estimated Sérgio P. Braz Dep. de Fitotecnia Univ. Federal Rural do Rio de Janeiro BR 465, km 07 Seropédica, 23890-000, RJ, Brazil Segundo Urquiaga Bruno J.R. Alves Claudia P. Jantalia Ana Paula Guimarães Embrapa Agrobiologia Rodovia BR 465, km 07 Seropédica, 23891-000, RJ, Brazil Camila A. dos Santos Sashia C. dos Santos Érika F. Machado Pinheiro Dep. de Solos Univ. Federal Rural do Rio de Janeiro BR 465, km 07 Seropédica, 23890-000, RJ, Brazil Robert M. Boddey* Embrapa Agrobiologia Rodovia BR 465, km 07 Seropédica, 23891-000, RJ, Brazil In the central savannah (Cerrados) region of Brazil approximately 50 Mha are occupied by Brachiaria pastures, most of which are classifed as degraded. There are few reliable data on soil C stocks under planted pastures in this region and how soil C has been affected by their establishment and subse- quent decline in productivity. This study was performed to compare soil C stocks under native Cerrado vegetation (NV) and productive (PP) and degraded pastures (DP) at four sites (chronosequences). Soil texture, bulk density, and 13 C abundance were investigated as candidate indicators for validation of the chronosequences. Productivity of the pastures at each site was evaluated using forage regrowth, existing and deposited litter, and the light fraction of soil organic matter (SOM). At all sites, the soil C stocks were higher under the PP than under the neighboring NV, and stocks under the DP were intermediate or very similar to the stocks under the NV. Soil 13 C abundance and C to N ratio suggested that SOM derived from NV was lost at a very low rate except in the surface layers (0–20 cm) and that soil C lost as pastures declined in productivity was principally derived from the pasture grass Brachiaria. The difference between soil C stocks under NV and PP was only 6 to 7 Mg C ha -1 at two sites with lower clay content (11 and 16%, respectively) but reached 12 Mg C ha -1 at Site C (46% clay) and 47 Mg C ha -1 at Site D (67% clay). Abbreviations: DP, degraded pastures; LWG, live weight gain; MBC, microbial biomass carbon; MG, Minas Gerais; MS, Mato Grosso do Sul; NV, native Cerrado vegetation; PP, productive pastures; SOM, soil organic matter; SP, São Paulo. Published May 10, 2013